Welding process for joining a metal body and a semiconducting body composed of metallic and ceramic material



Patented June 10, 1952 VJELDING PROCESS FOR JOINING A METAL BODY AND A SEMICONDUCTING BODY COMPOSEI) OF METALLIC AND CERAMIC MATERIAL Hermann Federspiel, Terlano, Italy No Drawing. Application May 19, 1949, Serial No. 94,268. In Italy April 26, 1948' 7 Claims.

This invention relates to a welding process for joining a metal body and a semi-conducting body composed of metallic and ceramic material. More particularly, the invention relates to a welding process for Welding a metal body to a semiconducting body in which the metallic component is comparatively small relative to the ceramic component.

As will be apparent, semi-conducting bodies with a small metallic component have predominantly ceramic characteristics rather than metallic characteristics. Practical tests and analysis show that the welding of a semi-conducting body of this type to a metal body offers considerable difliculties, particularly when electric welding is employed, by reason of the low con ductivity of the semi-conducting body.

A strong and reliable welding joint between a. metal body and a semi-conducting body of the general type, above referred to, is required in industry in many fields of application, particularly in the field of electrical engineering to connect a resistor made of or comprising semiconducting material to a metal connector. It will be evident that for such applications strong and intimate connection is required, both for physical and electrical reasons.

One of the preferred fields of application of the present invention is the welding of connectors to semi-conducting resistors of the capillary type, described in the co-pending application Ser. No. 772,194, filed September 4, 1947.

One of the objects of the invention is to provide a novel and improved process for welding together strongly and intimately a metal body and a semiconducting body containing a minor portion of metallic material and a major portion of ceramic material.

Another more specific object of the invention is to provide a novel and improved welding process by which the metallic content of the portion of the semi-conductor adjacent to the welding area or spot proper is increased. By such increase of the metallic content in a portion of the semiconducting body, the transition from the purely metallic material of the metal body to the material of the semi-conducting body having only a small metallic content becomes more gradual. In other words, a semi-conducting body treated according to the invention includes zones having the original composition, that is, a low metallic content, and zones having an increased metallic content, the latter zones or zone facing the metal body. As a result, a mechanically strong, highly conducting and temperature resistant welding joint between the metal body and the semiconducting body can be obtained.- According to the invention, the aforementioned-objects and advantages and other objects andadvantages which may be pointed out hereinafter are attained by joining the two bodies by a reduction welding process. The applied reduction welding process can either be carried out byelectric welding, by means of an electric arc or by gas welding by means of a reducing flame.

In case of electric welding, it is advantageous to initiate the fusing or melting of the proper portion of thesemi-conducting body by applying a welding voltage higher than conventionally used for welding purposes. It has further been found that particularly advantageous results can be obtained when the ceramic component of the semiconducting body comprises an oxide of the type, the electric resistance of which decreases with increasing temperature. As electrode, a carbon electrode is preferably used.

The reduction efiect, both for gas welding and electric welding, can be further improved by directing a current of a reducing gas against the welding area or welding spot during the welding operation.

In case of electric welding, it is often advantageous to preheat the welding area or spot.

By an example the process of fabrication should be described:

An electric resistor body, made of 20 weight per cent chrome-oxide, weight per cent manganese-oxide and 20 weight per cent ceramicplastic cement, sintered in lightly reducing atmosphere, and consisting of chrome-oxide, manganese-oxide, ceramic cement and 0.3 weight per cent metal will be provided on both ends with connection terminals of iron for the currentconduction.

The connection terminals and the ceramic body corresponding to the explanations of the invention claims, should be connected together by a welding process.

For the welding purpose, the terminals and a carbon electrode will be connected to a voltage source and an are produced between terminal and ceramic material on one side and the carbon electrode on the other side, the arc melting parts of the metal-terminals and of the ceramic body.

The are will be extinguished when the joint between ceramic body and the metal terminal is filled in with fluid material.

What is claimed is:

1. A welding process for joining a metal body and a semi-conductive body, the latter comprising tive portion of the semi-conductive body is transformed into metal in its elemental form and until molten metal of the said portions forms a joint between the same.

2. In the welding process as defined in claim 1 the additional step of directing a stream of a reducing gas against the said portions to be welded together.

3. A welding process as defined in claim 1, wherein said major component of the semiconductive body includes a metal oxide having a negative resistance coefficient.

4. A welding process for joining a metal conductor and a semi-conductive resistance element, the latter comprising in an intimate mixture a minor component of a metal and a major component composed of metal oxide and ceramic material, the said process comprising the steps of placing said conductor and said resistance element in an abutting position, and subjecting the abutting portions of the conductor and the resistance element to a welding temperature in the presence of a reducing atmosphere until metal contained in the respective portion of the resistance element is transformed into metal in its elemental form and until molten metal of the abutting portions of the conductor and the respective element forms a joint between the same.

5. A welding process as defined in claim 1, wherein said welding temperature is generated by an electric are.

6. In a heating process as defined in claim 5, the additional step of preheating the abutting portions of the conductor and the resistance element.

7. A Welding process as defined in claim 1, wherein the welding temperature is generated by a gas fiame.

HERMANN FEDERSPIEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 873,328 Price Dec. 10, 1907 1,884,665 Greiner Oct. 25, 1932 2,167,431 Bowie July 25, 1939 2,184,847 Pearson Dec. 26, 1939 2,271,995 Baroni Feb. 3, 1942 2,431,474 Gaudenzi Nov. 25, 1947 2,496,346 Haayman Feb. 7, 1950 FOREIGN PATENTS Number Country Date 595,007 Great Britain Nov. 25, 1947 

1. A WELDING PROCESS FOR JOINING A METAL BODY AND A SEMI-CONDUCTIVE BODY, THE LATTER COMPRISING IN AN INTIMATER MIXTURE A MINOR COMPONENT OF A METAL AND A MAJOR COMPONENT COMPOSED OF METAL OXIDE AND CERAMIC MATERIAL, THE SAID PROCESS COMPRISING THE STEPS OF PLACING THE PORTIONS OF THE TWO BODIES AT WHICH THE SAME ARE TO BE WELDED TOGETHER IN A CLOSE SPECIAL RELATIONSHIP, AND SUBJECTING THE SAID TWO PORTIONS TO A WELDING TEMPERATURE IN THE PRESENCE OF A REDUCING ATMOSPHERE UNTIL METAL OXIDE CONTAINED IN THE RESPECTIVE PORTION OF THE SEMI-CONDUCTIVE BODY IS TRANSFORMED INTO META IN ITS ELEMENTAL FORM AND UNTIL MOLTEN METAL OF THE SAID PORTIONS FORM A JOINT BETWEEN THE SAME. 